WITH t AS
(
SELECT 1 c1, 1 c2 FROM dual
UNION ALL SELECT 1.567, 2 FROM dual
UNION ALL SELECT 3.4, 3 FROM dual
UNION ALL SELECT 0, 0 FROM dual
)
SELECT c1, c2
     , RTRIM(TO_CHAR(c1, 'fm990.'||LPAD('0', c2, '0')), '.') c3
  FROM t
;

 
WITH t(n, s) AS(
   SELECT 1, 1 FROM dual
UNION ALL SELECT 1.567, 2 FROM dual
UNION ALL SELECT 3.4, 3 FROM dual
)
SELECT to_char(round(n, s), 'FM999'||decode(s, 0, '', RPAD('.', (s+1), '0')))
 FROM t
 

항상 아래 마농님이 댓글로 마무리가 되지만..
전 챙피해도 쓰는데... ㅋ